phage titration

Need help on phage titration.
When deluting a concentrated phage stock (Lambda gt11) containing a cDNA
I get plaques at high titer when spredding over 1000 phages on a plate
(plaques are touching each other) and at further delution I get no more
plaques.
Titration of an other phage (Lambda Gem) does not show any problem.
Hope someone can help
Sincerely Hannes